Neuroimaging research finds that people often consider drug addicts and homeless people to be sub-human.

You may fancy yourself a lover of all humanity, but according to a new study out of Princeton University, when confronted with extreme social outcasts, such as drug addicts and homeless people, your brain may unconsciously categorize them as less than human.

Neuroimaging research to be published in the October issue of Psychological Science shows that the stereotyping of groups as being sub-human can happen on an unconscious, neurological level, even when a person is not outwardly repulsed.

“People spontaneously categorize other people into ‘us’ and ‘them’ and they do that within milliseconds of encountering other people,” said Princeton psychologist Susan Fiske, a co-author of the study.

Social research has shown that people evaluate people unlike them according to two scales: how nice, or warm, they appear and how smart, or competent, they seem. Some social groups are commonly viewed as being low in competence and high in warmth (the elderly), while others are stereotyped as being high in competence but low in warmth (the wealthy). Social groups that are stereotyped as having neither warmth nor competence—like drug addicts—are often judged to be both hostile and stupid.

“All behavioral studies have indicated that when someone views a social group as low in both warmth and competence, they view them with contempt and disgust,” said graduate student Lasana Harris, another co-author on the study. “Brain imaging gives us another way to get at that phenomenon.”

To determine whether neurological reactions would reinforce the behavioral research, Harris and Fiske monitored the activity of the medial pre-frontal cortex (MPFC) via fMRI, while showing subjects pictures of people who represented different social groups, including the elderly, the wealthy, American Olympians and drug addicts. The MPFC is a brain region involved in social processing that is activated when someone thinks about a person—either himself or someone else—and it appears to be engaged in all forms of social cognition, said Harris.

When the study participants viewed pictures of social groups that are classically stereotyped as being high in warmth, competence or both—like the elderly, the wealthy and Olympians—their MPFC activity increased from a baseline level. But when people saw photos of homeless people and drug addicts, groups that are often stereotyped as being low in both warmth and competence, there was very little activity in that particular brain region.

Because the MPFC usually responds when a person encounters another human being, said Fiske, the finding suggests that the subjects’ brains were processing such outcasts as something other than human.

“It’s shocking,” she said. “The disgust reaction and the lowered medial pre-frontal cortex reaction is really getting close to saying, ‘This isn’t a person whose mental state we have to think about. This is barely even a person.’”

In fact, the pattern of brain activity induced by pictures of drug addicts and homeless people matched the pattern of brain activity resulting from photos of objects designed to provoke disgust, such as an overflowing toilet.

Nick Haslam, a psychologist who studies dehumanization at Australia’s University of Melbourne, called Harris’s and Fiske’s research innovative and noted their research is the first to explore this phenomenon with the tools of modern neuroscience.

When people are dehumanized, Haslam wrote in a paper, they no longer seem to evoke compassion from others. Further, dehumanization may play a role in more overt discrimination.

But, according to Haslam, it’s too early to say how the brain activity Fiske and Harris observed could correlate with conscious prejudice or actual behavior.

“I suspect the connections will be rather weak,” Haslam said. “People who have very negative or dehumanizing responses to particular groups may try to control or counteract their automatic responses and behave in unprejudiced ways.”

Still, brain imaging presents a new opportunity to study perceptions people may be uncomfortable admitting to researchers.

“Nobody’s going to say that they think homeless people are disgusting,” Fiske said. “We are interested in trying to get at it in a way that gets around issues of self-report and in ways that even people aren’t aware of themselves.”

Originally published July 21, 2006

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